✅ SQL Programming: Handling NULL Values 🛠️

Missing data is common in databases. COALESCE() helps you fill in defaults and avoid null-related issues.

1️⃣ What is COALESCE?
Returns the first non-null value in a list.

SELECT name, COALESCE(phone, 'Not Provided') AS contact  
FROM customers;

✅ If phone is NULL, it shows ‘Not Provided’.

2️⃣ COALESCE with Calculations
Prevent nulls from breaking math.

SELECT name, salary, COALESCE(bonus, 0) AS bonus,  
       salary + COALESCE(bonus, 0) AS total_income  
FROM employees;

✅ If bonus is NULL, treat it as 0 to compute total.

3️⃣ Nested COALESCE
Use multiple fallback options.

SELECT name, COALESCE(email, alt_email, 'No Email') AS contact_email  
FROM users;

✅ Checks email, then alt_email, then default text.

4️⃣ COALESCE in WHERE clause
Filter even when data has nulls.

SELECT *  
FROM products  
WHERE COALESCE(category, 'Uncategorized') = 'Electronics';

🎯 Use COALESCE When You Want To:
• Replace NULLs with defaults
• Keep math & filters working
• Avoid errors in reports or dashboards

📝 Practice Tasks:
1. Replace nulls in city with ‘Unknown’
2. Show total amount = price + tax (tax may be null)
3. Replace nulls in description with ‘No Info Available’

✅ Solution for Practice Tasks 👇

1️⃣ Replace NULLs in city with 'Unknown'

SELECT name, COALESCE(city, 'Unknown') AS city  
FROM customers;

2️⃣ Show total amount = price + tax (tax may be NULL)

SELECT product_name, price, COALESCE(tax, 0) AS tax,  
       price + COALESCE(tax, 0) AS total_amount  
FROM products;

3️⃣ Replace NULLs in description with 'No Info Available'

SELECT product_name, COALESCE(description, 'No Info Available') AS description  
FROM products;

💬 Tap ❤️ for more!